This invention relates to an optical amplifier repeater that is inserted into the optical transmission line to compensate the attenuation of optical signal on the optical transmission line and to supervise the optical transmission line.
Regarding the prior art to the invention, for example, Japanese patent application laid-open No. 6-204949 (1994) (hereinafter referred as xe2x80x98prior art 1xe2x80x99) titled xe2x80x9cOptical Transmission Systemxe2x80x9d discloses an optical amplifier repeater.
FIG. 1 is a block diagram showing the composition of the optical amplifier repeater in prior art 1. In FIG. 1, 1 is the optical amplifier repeater, 2a is a first optical amplifier, 2b is a second optical amplifier, 3a is a first optical coupler, 3b is a second optical coupler, 4a is a first optical attenuator, and 4b is a second optical attenuator.
The up optical-fiber transmission line and down optical-fiber transmission line comprise opposed lines.
FIG. 2 is a block diagram showing the operation of the optical amplifier repeater 1. In FIG. 2, like parts are indicated by like reference numerals as used in FIG. 1. Optical signals with four wavelengths xcex1 to xcex4 transmitted through the up optical-fiber transmission line are wavelength-multiplexed, and supervisory signal light with a wavelength of xcexsv1 is added thereto.
Optical signal on the up optical-fiber transmission line is output through the first optical coupler 3a, the first optical attenuator 4a and the second optical coupler 3b to the down optical-fiber transmission line. Supervisory signal light output to the down optical-fiber transmission line is received and measured by a transmission terminal on the up optical-fiber transmission line, whereby the monitoring of the transmission line is conducted.
However, in the above monitoring method explained in FIG. 2, there is a problem as described below. Namely, since losses at the first optical coupler 3a, the first optical attenuator 4a and the second optical coupler 3b are almost equal for each wavelength, optical signal with wavelengths on the up optical-fiber transmission line is transferred to the down optical-fiber transmission line while having the ratio of intensity only moderately changed. Thus, main signal transferred from the up optical-fiber transmission line to the down optical-fiber transmission line interferes with the main signal transferred through the down optical-fiber transmission line, reducing the signal-to-noise ratio.
Although the intensity of main signal light transferred from the up optical-fiber transmission line to the down optical-fiber transmission line may be sufficiently weakened to prevent the S/N ratio from being reduced, the intensity of supervisory signal light transferred from the up optical-fiber transmission line to the down optical-fiber transmission is also weakened. Therefore, there is a problem in that a high-precision reception circuit is needed to receive such supervisory signal light.
Also, Japanese patent application laid-open No. 8-181656 (1996) (hereinafter referred as xe2x80x98prior art 2xe2x80x99) titled xe2x80x9cMonitoring Device for Optical WDM Communication Transmission Linexe2x80x9d discloses another prior art optical amplifier repeater.
FIG. 3 is a block diagram showing the composition of the optical amplifier repeater in the second prior art. In FIG. 3, like or corresponding parts are indicated by like reference numerals as used in FIG. 1 and the explanations thereof are omitted.
Meanwhile, in all of the drawings attached to this specification, like or corresponding parts are indicated by like reference numerals and the explanations thereof are omitted herein.
In FIG. 3, 20a is a first optical bandpass filter and 20b is a second optical bandpass filter. These optical bandpass filters are designed to pass only supervisory signal light.
FIG. 4 is a block diagram showing the operation of the optical amplifier repeater 1 in FIG. 3. Although, compared with the operation in prior art 1 in FIG. 2, the intensity of main signal light transferred from the up optical-fiber transmission line to the down optical-fiber transmission line is attenuated by the selectivity of the optical bandpass filter, main signal light with wavelengths near the supervisory signal light is not sufficiently attenuated.
This is because the transmission band of the optical bandpass filter is difficult to sharply define sufficiently (see the transmittance of optical filter in FIG. 4). Therefore, there is a problem in that the main signal light, with a wavelength adjacent to the supervisory signal light, interferes with the main signal light transmitted through the down optical-fiber transmission line to deteriorate its characteristic.
In order to prevent the characteristic from deteriorating, the wavelength of supervisory signal light is located apart from the wavelength of the main signal light. However, it is then required to undesirably widen the amplification wavelength band of the optical amplifier.
Accordingly, it is an object of the invention to provide an optical amplifier repeater where only the supervisory signal light can be transferred from the up optical-fiber transmission line to the down optical-fiber transmission line.
It is a further object of the invention to provide an optical amplifier repeater that supervisory signal light can be transferred to the opposed transmission line from both the output side and input side of optical amplifier.
It is a still further object of the invention to provide an optical amplifier repeater that the return circuit between the up and down optical-fiber transmission lines is connected by one optical transmission line.
According to the invention, an optical amplifier repeater, comprises:
a first optical amplifier that amplifies main signal light and supervisory signal light transmitted on an up optical-fiber transmission line;
a second optical amplifier that amplifies main signal light and supervisory signal light transmitted on a down optical-fiber transmission line;
a transfer means that transfers part of supervisory signal light transmitted on the up optical-fiber transmission line onto the down optical-fiber transmission line, and that transfers part of supervisory signal light transmitted on the down optical-fiber transmission line onto the up optical-fiber transmission line;
wherein the transfer means comprises an optical amplifier output side transfer means that transfers supervisory signal light reflected by a first light-reflecting means inserted to the output side of the first optical amplifier to the output side of the second optical amplifier, and transfers supervisory signal light reflected by a second light-reflecting means inserted to the output side of the second optical amplifier to the output side of the first optical amplifier.
According to another aspect of the invention, an optical amplifier repeater, comprises:
a first optical amplifier that amplifies main signal light and supervisory signal light transmitted on an up optical-fiber transmission line;
a second optical amplifier that amplifies main signal light and supervisory signal light transmitted on a down optical-fiber transmission line;
a transfer means that transfers part of supervisory signal light transmitted on the up optical-fiber transmission line onto the down optical-fiber transmission line, and that transfers part of supervisory signal light transmitted on the down optical-fiber transmission line onto the up optical-fiber transmission line;
wherein the transfer means comprises an optical amplifier input side transfer means that transfers supervisory signal light reflected by a third light-reflecting means inserted to the input side of the first optical amplifier to the output side of the second optical amplifier, and transfers supervisory signal light reflected by a fourth light-reflecting means inserted to the input side of the second optical amplifier to the output side of the first optical amplifier.
According to another aspect of the invention, an optical amplifier repeater, comprises:
a first optical amplifier that amplifies main signal light and supervisory signal light transmitted on an up optical-fiber transmission line;
a second optical amplifier that amplifies main signal light and supervisory signal light transmitted on a down optical-fiber transmission line;
a transfer means that transfers part of supervisory signal light transmitted on the up optical-fiber transmission line onto the down optical-fiber transmission line, and that transfers part of supervisory signal light transmitted on the down optical-fiber transmission line onto the up optical-fiber transmission line;
wherein the transfer means comprises an optical amplifier output side transfer means that transfers supervisory signal light reflected by a first light-reflecting means inserted to the output side of the first optical amplifier to the output side of the second optical amplifier, and transfers supervisory signal light reflected by a second light-reflecting means inserted to the output side of the second optical amplifier to the output side of the first optical amplifier, and an optical amplifier input side transfer means that transfers supervisory signal light reflected by a third light-reflecting means inserted to the input side of the first optical amplifier to the output side of the second optical amplifier, and transfers supervisory signal light reflected by a fourth light-reflecting means inserted to the input side of the second optical amplifier to the output side of the first optical amplifier.
According to another aspect of the invention, an optical amplifier repeater, comprises:
a first optical amplifier that amplifies main signal light and supervisory signal light transmitted on an up optical-fiber transmission line;
a second optical amplifier that amplifies main signal light and supervisory signal light transmitted on a down optical-fiber transmission line;
a transfer means that transfers part of supervisory signal light transmitted on the up optical-fiber transmission line onto the down optical-fiber transmission line, and that transfers part of supervisory signal light transmitted on the down optical-fiber transmission line onto the up optical-fiber transmission line;
wherein the transfer means comprises a first light-reflecting means that is connected to the forward output port of the second-order side transmission line of a first optical coupler disposed on the output side of the first optical amplifier, a second light-reflecting means that is connected to the forward output port of the second-order side transmission line of a second optical coupler disposed on the output side of the second optical amplifier, a third light-reflecting means that is connected to the forward output port of the second-order side transmission line of a third optical coupler disposed on the input side of the first optical amplifier, a fourth light-reflecting means that is connected to the forward output port of the second-order side transmission line of a fourth optical coupler disposed on the input side of the second optical amplifier, an optical transmission line that connects between the reverse output port of the second-order side transmission line of the fourth optical coupler and the reverse output port of the second-order side transmission line of the first optical coupler, and an optical transmission line that connects between the reverse output port of the second-order side transmission line of the second optical coupler and the reverse output port of the second-order side transmission line of the third optical coupler.